In recent years, systems which distribute digital copyrighted works, such as music, images, and games, through the Internet or digital broadcasting have been developed. Some of them have entered a commercial stage. In connection with the content distribution, methods of controlling content usages are also considered in order to limit the number of reproduction times, transfers, and duplicates of the distributed content from the viewpoint of copyright protection.
Conventionally, a server distributes information that includes a usage rule and a content key required when using the content (this information is referred to as the “license” hereafter). With the license distributed from the server, a home terminal device is modeled to use the content so as to perform reproduction and so forth.
As the usage rule, an allowed number of content usages and an allowed cumulative time period of a content usage are set, for example. In this case, the usage rule needs to be updated in accordance with the amount that the terminal device has been using the content.
For example, Patent Reference 1 describes a contents using device which allows a content usage in the case where the number of usages is other than 0 when a terminal device starts to use content, and then subtracts one from the number of usages at the end of the content usage.    Patent Reference 1: Japanese Laid-Open Patent Application No. 2002-008309